Try letting it run for an extended period of time, more than a minute. Sometimes, if it gets a large page, it will slow down considerably, or do chunks of the site. I have a fairly large (170+) page site, and for a few pages, it will decrease in speed incredibly, but if I leave it be, it will continue to work.
With the site being locked, that means that it is still working at spidering the site. Just give it time, it'll get through. Just a bit slow perhaps
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